/*
 * DFA routines
 * This file is #included by regexec.cpp.
 *
 * Copyright (c) 1998, 1999 Henry Spencer.	All rights reserved.
 *
 * Development of this software was funded, in part, by Cray Research Inc.,
 * UUNET Communications Services Inc., Sun Microsystems Inc., and Scriptics
 * Corporation, none of whom are responsible for the results.  The author
 * thanks all of them.
 *
 * Redistribution and use in source and binary forms -- with or without
 * modification -- are permitted for any purpose, provided that
 * redistributions in source form retain this entire copyright notice and
 * indicate the origin and nature of any modifications.
 *
 * I'd appreciate being given credit for this package in the documentation
 * of software which uses it, but that is not a requirement.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
 * HENRY SPENCER BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * src/common/backend/regex/rege_dfa.cpp
 *
 */

/*
 * longest - longest-preferred matching engine
 * return endpoint, or NULL
 */
static chr* longest(struct vars* v,        /* used only for debug and exec flags */
    struct dfa* d, chr* start, /* where the match should start */
    chr* stop,                 /* match must end at or before here */
    int* hitstopp)             /* record whether hit v->stop, if non-NULL */
{
    chr* cp = NULL;
    chr* realstop = (stop == v->stop) ? stop : (stop + 1);
    color co;
    struct sset* css = NULL;
    struct sset* ss = NULL;
    chr* post = NULL;
    int i;
    struct colormap* cm = d->cm;

    /* initialize */
    css = initialize(v, d, start);
    cp = start;
    if (hitstopp != NULL)
        *hitstopp = 0;

    /* startup */
    FDEBUG(("+++ startup +++\n"));
    if (cp == v->start) {
        co = d->cnfa->bos[(v->eflags & REG_NOTBOL) ? 0 : 1];
        FDEBUG(("color %ld\n", (long)co));
    } else {
        co = GETCOLOR(cm, *(cp - 1));
        FDEBUG(("char %c, color %ld\n", (char)*(cp - 1), (long)co));
    }
    css = miss(v, d, css, co, cp, start);
    if (css == NULL)
        return NULL;
    css->lastseen = cp;

    /* main loop */
    if (v->eflags & REG_FTRACE)
        while (cp < realstop) {
            FDEBUG(("+++ at c%d +++\n", (int)(css - d->ssets)));
            co = GETCOLOR(cm, *cp);
            FDEBUG(("char %c, color %ld\n", (char)*cp, (long)co));
            ss = css->outs[co];
            if (ss == NULL) {
                ss = miss(v, d, css, co, cp + 1, start);
                if (ss == NULL)
                    break; /* NOTE BREAK OUT */
            }
            cp++;
            ss->lastseen = cp;
            css = ss;
        }
    else
        while (cp < realstop) {
            co = GETCOLOR(cm, *cp);
            ss = css->outs[co];
            if (ss == NULL) {
                ss = miss(v, d, css, co, cp + 1, start);
                if (ss == NULL)
                    break; /* NOTE BREAK OUT */
            }
            cp++;
            ss->lastseen = cp;
            css = ss;
        }

    /* shutdown */
    FDEBUG(("+++ shutdown at c%d +++\n", (int)(css - d->ssets)));
    if (cp == v->stop && stop == v->stop) {
        if (hitstopp != NULL)
            *hitstopp = 1;
        co = d->cnfa->eos[(v->eflags & REG_NOTEOL) ? 0 : 1];
        FDEBUG(("color %ld\n", (long)co));
        ss = miss(v, d, css, co, cp, start);
        /* special case:  match ended at eol? */
        if (ss != NULL && (ss->flags & POSTSTATE))
            return cp;
        else if (ss != NULL)
            ss->lastseen = cp; /* to be tidy */
    }

    /* find last match, if any */
    post = d->lastpost;
    for (ss = d->ssets, i = d->nssused; i > 0; ss++, i--)
        if ((ss->flags & POSTSTATE) && post != ss->lastseen && (post == NULL || post < ss->lastseen))
            post = ss->lastseen;
    if (post != NULL) /* found one */
        return post - 1;

    return NULL;
}

/*
 * shortest - shortest-preferred matching engine
 * return endpoint, or NULL
 */
static chr* shortest(struct vars* v, struct dfa* d, chr* start, /* where the match should start */
    chr* min,      /* match must end at or after here */
    chr* max,      /* match must end at or before here */
    chr** coldp,   /* store coldstart pointer here, if nonNULL */
    int* hitstopp) /* record whether hit v->stop, if non-NULL */
{
    chr* cp = NULL;
    chr* realmin = (min == v->stop) ? min : (min + 1);
    chr* realmax = (max == v->stop) ? max : (max + 1);
    color co;
    struct sset* css = NULL;
    struct sset* ss = NULL;
    struct colormap* cm = d->cm;

    /* prevent "uninitialized variable" warnings */
    if (coldp != NULL)
        *coldp = NULL;
    if (hitstopp != NULL)
        *hitstopp = 0;

    /* initialize */
    css = initialize(v, d, start);
    if (css == NULL)
        return NULL;
    cp = start;
    if (hitstopp != NULL)
        *hitstopp = 0;

    /* startup */
    FDEBUG(("--- startup ---\n"));
    if (cp == v->start) {
        co = d->cnfa->bos[(v->eflags & REG_NOTBOL) ? 0 : 1];
        FDEBUG(("color %ld\n", (long)co));
    } else {
        co = GETCOLOR(cm, *(cp - 1));
        FDEBUG(("char %c, color %ld\n", (char)*(cp - 1), (long)co));
    }
    css = miss(v, d, css, co, cp, start);
    if (css == NULL)
        return NULL;
    css->lastseen = cp;
    ss = css;

    /*
     * This is the main text-scanning loop.  It seems worth having two copies
     * to avoid the overhead of REG_FTRACE tests here, even in REG_DEBUG
     * builds, when you're not actively tracing.
     */
#ifdef REG_DEBUG
    if (v->eflags & REG_FTRACE) {
        while (cp < realmax) {
            FDEBUG(("--- at c%d ---\n", (int)(css - d->ssets)));
            co = GETCOLOR(cm, *cp);
            FDEBUG(("char %c, color %ld\n", (char)*cp, (long)co));
            ss = css->outs[co];
            if (ss == NULL) {
                ss = miss(v, d, css, co, cp + 1, start);
                if (ss == NULL)
                    break; /* NOTE BREAK OUT */
            }
            cp++;
            ss->lastseen = cp;
            css = ss;
            if ((ss->flags & POSTSTATE) && cp >= realmin)
                break; /* NOTE BREAK OUT */
        }
    } else
#endif
    {
        while (cp < realmax) {
            co = GETCOLOR(cm, *cp);
            ss = css->outs[co];
            if (ss == NULL) {
                ss = miss(v, d, css, co, cp + 1, start);
                if (ss == NULL)
                    break; /* NOTE BREAK OUT */
            }
            cp++;
            ss->lastseen = cp;
            css = ss;
            if ((ss->flags & POSTSTATE) && cp >= realmin)
                break; /* NOTE BREAK OUT */
        }
    }

    if (ss == NULL)
        return NULL;

    if (coldp != NULL) /* report last no-progress state set, if any */
        *coldp = lastcold(v, d);

    if ((ss->flags & POSTSTATE) && cp > min) {
        Assert(cp >= realmin);
        cp--;
    } else if (cp == v->stop && max == v->stop) {
        co = d->cnfa->eos[(v->eflags & REG_NOTEOL) ? 0 : 1];
        FDEBUG(("color %ld\n", (long)co));
        ss = miss(v, d, css, co, cp, start);
        /* match might have ended at eol */
        if ((ss == NULL || !(ss->flags & POSTSTATE)) && hitstopp != NULL)
            *hitstopp = 1;
    }

    if (ss == NULL || !(ss->flags & POSTSTATE))
        return NULL;

    return cp;
}

/*
 * matchuntil - incremental matching engine
 *
 * This is meant for use with a search-style NFA (that is, the pattern is
 * known to act as though it had a leading .*).  We determine whether a
 * match exists starting at v->start and ending at probe.  Multiple calls
 * require only O(N) time not O(N^2) so long as the probe values are
 * nondecreasing.  *lastcss and *lastcp must be initialized to NULL before
 * starting a series of calls.
 *
 * Returns 1 if a match exists, 0 if not.
 * Internal errors also return 0, with v->err set.
 */
static int matchuntil(struct vars* v, struct dfa* d, chr* probe, /* we want to know if a match ends here */
    struct sset** lastcss,                                       /* state storage across calls */
    chr** lastcp)                                                /* state storage across calls */
{
    chr* cp = *lastcp;
    color co;
    struct sset* css = *lastcss;
    struct sset* ss = NULL;
    struct colormap* cm = d->cm;

    /* initialize and startup, or restart, if necessary */
    if (cp == NULL || cp > probe) {
        cp = v->start;
        css = initialize(v, d, cp);
        if (css == NULL)
            return 0;

        FDEBUG((">>> startup >>>\n"));
        co = d->cnfa->bos[(v->eflags & REG_NOTBOL) ? 0 : 1];
        FDEBUG(("color %ld\n", (long)co));

        css = miss(v, d, css, co, cp, v->start);
        if (css == NULL)
            return 0;
        css->lastseen = cp;
    } else if (css == NULL) {
        /* we previously found that no match is possible beyond *lastcp */
        return 0;
    }
    ss = css;

    /*
     * This is the main text-scanning loop.  It seems worth having two copies
     * to avoid the overhead of REG_FTRACE tests here, even in REG_DEBUG
     * builds, when you're not actively tracing.
     */
#ifdef REG_DEBUG
    if (v->eflags & REG_FTRACE) {
        while (cp < probe) {
            FDEBUG((">>> at c%d >>>\n", (int)(css - d->ssets)));
            co = GETCOLOR(cm, *cp);
            FDEBUG(("char %c, color %ld\n", (char)*cp, (long)co));
            ss = css->outs[co];
            if (ss == NULL) {
                ss = miss(v, d, css, co, cp + 1, v->start);
                if (ss == NULL)
                    break; /* NOTE BREAK OUT */
            }
            cp++;
            ss->lastseen = cp;
            css = ss;
        }
    } else
#endif
    {
        while (cp < probe) {
            co = GETCOLOR(cm, *cp);
            ss = css->outs[co];
            if (ss == NULL) {
                ss = miss(v, d, css, co, cp + 1, v->start);
                if (ss == NULL)
                    break; /* NOTE BREAK OUT */
            }
            cp++;
            ss->lastseen = cp;
            css = ss;
        }
    }

    *lastcss = ss;
    *lastcp = cp;

    if (ss == NULL)
        return 0; /* impossible match, or internal error */

    /* We need to process one more chr, or the EOS symbol, to check match */
    if (cp < v->stop) {
        FDEBUG((">>> at c%d >>>\n", (int)(css - d->ssets)));
        co = GETCOLOR(cm, *cp);
        FDEBUG(("char %c, color %ld\n", (char)*cp, (long)co));
        ss = css->outs[co];
        if (ss == NULL)
            ss = miss(v, d, css, co, cp + 1, v->start);
    } else {
        Assert(cp == v->stop);
        co = d->cnfa->eos[(v->eflags & REG_NOTEOL) ? 0 : 1];
        FDEBUG(("color %ld\n", (long)co));
        ss = miss(v, d, css, co, cp, v->start);
    }

    if (ss == NULL || !(ss->flags & POSTSTATE))
        return 0;

    return 1;
}

/*
 * lastcold - determine last point at which no progress had been made
 * return endpoint, or NULL
 */
static chr* lastcold(struct vars* v, struct dfa* d)
{
    struct sset* ss = NULL;
    chr* nopr = NULL;
    int i;

    nopr = d->lastnopr;
    if (nopr == NULL)
        nopr = v->start;
    for (ss = d->ssets, i = d->nssused; i > 0; ss++, i--)
        if ((ss->flags & NOPROGRESS) && nopr < ss->lastseen)
            nopr = ss->lastseen;
    return nopr;
}

/*
 * newdfa - set up a fresh DFA
 */
static struct dfa* newdfa(
    struct vars* v, struct cnfa* cnfa, struct colormap* cm, struct smalldfa* sml) /* preallocated space, may be NULL */
{
    struct dfa* d = NULL;
    size_t nss = cnfa->nstates * 2;
    int wordsper = (cnfa->nstates + UBITS - 1) / UBITS;
    struct smalldfa* smallwas = sml;

    Assert(cnfa != NULL && cnfa->nstates != 0);

    if (nss <= FEWSTATES && cnfa->ncolors <= FEWCOLORS) {
        Assert(wordsper == 1);
        if (sml == NULL) {
            sml = (struct smalldfa*)MALLOC(sizeof(struct smalldfa));
            if (sml == NULL) {
                ERR(REG_ESPACE);
                return NULL;
            }
            errno_t rc = memset_s(sml, sizeof(struct smalldfa), 0, sizeof(struct smalldfa));
            securec_check(rc, "\0", "\0");
        }

        d = &sml->dfa;
        d->ssets = sml->ssets;
        d->statesarea = sml->statesarea;
        d->work = &d->statesarea[nss];
        d->outsarea = sml->outsarea;
        d->incarea = sml->incarea;
        d->cptsmalloced = 0;
        d->mallocarea = (smallwas == NULL) ? (char*)sml : NULL;
    } else {
        d = (struct dfa*)MALLOC(sizeof(struct dfa));
        if (d == NULL) {
            ERR(REG_ESPACE);
            return NULL;
        }
        d->ssets = (struct sset*)MALLOC(nss * sizeof(struct sset));
        d->statesarea = (unsigned*)MALLOC((nss + WORK) * wordsper * sizeof(unsigned));
        d->work = &d->statesarea[nss * wordsper];
        d->outsarea = (struct sset**)MALLOC(nss * cnfa->ncolors * sizeof(struct sset*));
        d->incarea = (struct arcp*)MALLOC(nss * cnfa->ncolors * sizeof(struct arcp));
        d->cptsmalloced = 1;
        d->mallocarea = (char*)d;
        if (d->ssets == NULL || d->statesarea == NULL || d->outsarea == NULL || d->incarea == NULL) {
            freedfa(d);
            ERR(REG_ESPACE);
            return NULL;
        }
    }

    d->nssets = (v->eflags & REG_SMALL) ? 7 : nss;
    d->nssused = 0;
    d->nstates = cnfa->nstates;
    d->ncolors = cnfa->ncolors;
    d->wordsper = wordsper;
    d->cnfa = cnfa;
    d->cm = cm;
    d->lastpost = NULL;
    d->lastnopr = NULL;
    d->search = d->ssets;

    /* initialization of sset fields is done as needed */
    return d;
}

/*
 * freedfa - free a DFA
 */
static void freedfa(struct dfa* d)
{
    if (d->cptsmalloced) {
        if (d->ssets != NULL)
            FREE(d->ssets);
        if (d->statesarea != NULL)
            FREE(d->statesarea);
        if (d->outsarea != NULL)
            FREE(d->outsarea);
        if (d->incarea != NULL)
            FREE(d->incarea);
    }

    if (d->mallocarea != NULL)
        FREE(d->mallocarea);
}

/*
 * hash - construct a hash code for a bitvector
 *
 * There are probably better ways, but they're more expensive.
 */
static unsigned hash(unsigned* uv, int n)
{
    int i;
    unsigned h;

    h = 0;
    for (i = 0; i < n; i++) {
        h ^= uv[i];
    }
    return h;
}

/*
 * initialize - hand-craft a cache entry for startup, otherwise get ready
 */
static struct sset* initialize(struct vars* v, /* used only for debug flags */
    struct dfa* d, chr* start)
{
    struct sset* ss = NULL;
    int i;

    /* is previous one still there? */
    if (d->nssused > 0 && (d->ssets[0].flags & STARTER)) {
        ss = &d->ssets[0];
    } else { /* no, must (re)build it */
        ss = getvacant(v, d, start, start);
        for (i = 0; i < d->wordsper; i++)
            ss->states[i] = 0;
        BSET(ss->states, d->cnfa->pre);
        ss->hash = HASH(ss->states, d->wordsper);
        Assert(d->cnfa->pre != d->cnfa->post);
        ss->flags = STARTER | LOCKED | NOPROGRESS;
        /* lastseen dealt with below */
    }

    for (i = 0; i < d->nssused; i++)
        d->ssets[i].lastseen = NULL;
    ss->lastseen = start; /* maybe untrue, but harmless */
    d->lastpost = NULL;
    d->lastnopr = NULL;
    return ss;
}

/*
 * miss - handle a cache miss
 * return NULL if goes to empty set
 */
static struct sset* miss(struct vars* v,  /* used only for debug flags */
    struct dfa* d, struct sset* css, pcolor co, chr* cp, /* next chr */
    chr* start) /* where the attempt got started */
{
    struct cnfa* cnfa = d->cnfa;
    int i;
    unsigned h;
    struct carc* ca = NULL;
    struct sset* p = NULL;
    int ispost;
    int noprogress;
    int gotstate;
    int dolacons;
    int sawlacons;

    /* for convenience, we can be called even if it might not be a miss */
    if (css->outs[co] != NULL) {
        FDEBUG(("hit\n"));
        return css->outs[co];
    }
    FDEBUG(("miss\n"));

    /* first, what set of states would we end up in? */
    for (i = 0; i < d->wordsper; i++) {
        d->work[i] = 0;
    }
    ispost = 0;
    noprogress = 1;
    gotstate = 0;
    for (i = 0; i < d->nstates; i++) {
        if (ISBSET(css->states, i)) {
            for (ca = cnfa->states[i]; ca->co != COLORLESS; ca++) {
                if (ca->co == co) {
                    BSET(d->work, ca->to);
                    gotstate = 1;
                    if (ca->to == cnfa->post) {
                        ispost = 1;
                    }
                    if (!(cnfa->stflags[ca->to] & CNFA_NOPROGRESS)) {
                        noprogress = 0;
                    }
                    FDEBUG(("%d -> %d\n", i, ca->to));
                }
            }
        }
    }
    dolacons = (gotstate) ? (cnfa->flags & HASLACONS) : 0;
    sawlacons = 0;
    while (dolacons) { /* transitive closure */
        dolacons = 0;
        for (i = 0; i < d->nstates; i++) {
            if (ISBSET(d->work, i)) {
                for (ca = cnfa->states[i]; ca->co != COLORLESS; ca++) {
                    if (ca->co < cnfa->ncolors) {
                        continue; /* NOTE CONTINUE */
                    }
                    sawlacons = 1;
                    if (ISBSET(d->work, ca->to)) {
                        continue; /* NOTE CONTINUE */
                    }
                    if (!lacon(v, cnfa, cp, ca->co)) {
                        continue; /* NOTE CONTINUE */
                    }
                    BSET(d->work, ca->to);
                    dolacons = 1;
                    if (ca->to == cnfa->post) {
                        ispost = 1;
                    }
                    if (!(cnfa->stflags[ca->to] & CNFA_NOPROGRESS)) {
                        noprogress = 0;
                    }
                    FDEBUG(("%d :> %d\n", i, ca->to));
                }
            }
        }
    }
    if (!gotstate) {
        return NULL;
    }
    h = HASH(d->work, d->wordsper);

    /* next, is that in the cache? */
    for (p = d->ssets, i = d->nssused; i > 0; p++, i--) {
        if (HIT(h, d->work, p, d->wordsper)) {
            FDEBUG(("cached c%d\n", (int)(p - d->ssets)));
            break; /* NOTE BREAK OUT */
        }
    }
    if (i == 0) { /* nope, need a new cache entry */
        p = getvacant(v, d, cp, start);
        Assert(p != css);
        for (i = 0; i < d->wordsper; i++) {
            p->states[i] = d->work[i];
        }
        p->hash = h;
        p->flags = (ispost) ? POSTSTATE : 0;
        if (noprogress) {
            p->flags |= NOPROGRESS;
        }
        /* lastseen to be dealt with by caller */
    }

    if (!sawlacons) { /* lookahead conds. always cache miss */
        FDEBUG(("c%d[%d]->c%d\n", (int)(css - d->ssets), co, (int)(p - d->ssets)));
        css->outs[co] = p;
        css->inchain[co] = p->ins;
        p->ins.ss = css;
        p->ins.co = (color)co;
    }
    return p;
}

/*
 * lacon - lookaround-constraint checker for miss()
 * return predicate:  constraint satisfied?
 */
static int lacon(struct vars* v, struct cnfa* pcnfa, /* parent cnfa */
    chr* cp, pcolor co) /* "color" of the lookaround constraint */
{
    int n;
    struct subre* sub = NULL;
    struct dfa* d = NULL;
    chr* end = NULL;
    int satisfied;

    /* Since this is recursive, it could be driven to stack overflow */
    if (STACK_TOO_DEEP(v->re)) {
        ERR(REG_ETOOBIG);
        return 0;
    }

    n = co - pcnfa->ncolors;
    Assert(n > 0 && n < v->g->nlacons && v->g->lacons != NULL);
    FDEBUG(("=== testing lacon %d\n", n));
    sub = &v->g->lacons[n];
    d = getladfa(v, n);
    if (d == NULL)
        return 0;
    if (LATYPE_IS_AHEAD(sub->subno)) {
        /* used to use longest() here, but shortest() could be much cheaper */
        end = shortest(v, d, cp, cp, v->stop, (chr**)NULL, (int*)NULL);
        satisfied = LATYPE_IS_POS(sub->subno) ? (end != NULL) : (end == NULL);
    } else {
        /*
         * To avoid doing O(N^2) work when repeatedly testing a lookbehind
         * constraint in an N-character string, we use matchuntil() which can
         * cache the DFA state across calls.	We only need to restart if the
         * probe point decreases, which is not common.  The NFA we're using is
         * a search NFA, so it doesn't mind scanning over stuff before the
         * nominal match.
         */
        satisfied = matchuntil(v, d, cp, &v->lblastcss[n], &v->lblastcp[n]);
        if (!LATYPE_IS_POS(sub->subno))
            satisfied = !satisfied;
    }

    FDEBUG(("=== lacon %d satisfied %d\n", n, satisfied));
    return satisfied;
}

/*
 * getvacant - get a vacant state set
 * This routine clears out the inarcs and outarcs, but does not otherwise
 * clear the innards of the state set -- that's up to the caller.
 */
static struct sset* getvacant(struct vars* v, /* used only for debug flags */
    struct dfa* d, chr* cp, chr* start)
{
    int i;
    struct sset* ss = NULL;
    struct sset* p = NULL;
    struct arcp ap;
    color co;

    ss = pickss(v, d, cp, start);
    Assert(!(ss->flags & LOCKED));

    /* clear out its inarcs, including self-referential ones */
    ap = ss->ins;
    while ((p = ap.ss) != NULL) {
        co = ap.co;
        FDEBUG(("zapping c%d's %ld outarc\n", (int)(p - d->ssets), (long)co));
        p->outs[co] = NULL;
        ap = p->inchain[co];
        p->inchain[co].ss = NULL; /* paranoia */
    }
    ss->ins.ss = NULL;

    /* take it off the inarc chains of the ssets reached by its outarcs */
    for (i = 0; i < d->ncolors; i++) {
        p = ss->outs[i];
        Assert(p != ss); /* not self-referential */
        if (p == NULL)
            continue; /* NOTE CONTINUE */
        FDEBUG(("del outarc %d from c%d's in chn\n", i, (int)(p - d->ssets)));
        if (p->ins.ss == ss && p->ins.co == i)
            p->ins = ss->inchain[i];
        else {
            struct arcp lastap = {NULL, 0};

            Assert(p->ins.ss != NULL);
            for (ap = p->ins; ap.ss != NULL && !(ap.ss == ss && ap.co == i); ap = ap.ss->inchain[ap.co])
                lastap = ap;
            Assert(ap.ss != NULL);
            lastap.ss->inchain[lastap.co] = ss->inchain[i];
        }
        ss->outs[i] = NULL;
        ss->inchain[i].ss = NULL;
    }

    /* if ss was a success state, may need to remember location */
    if ((ss->flags & POSTSTATE) && ss->lastseen != d->lastpost && (d->lastpost == NULL || d->lastpost < ss->lastseen))
        d->lastpost = ss->lastseen;

    /* likewise for a no-progress state */
    if ((ss->flags & NOPROGRESS) && ss->lastseen != d->lastnopr && (d->lastnopr == NULL || d->lastnopr < ss->lastseen))
        d->lastnopr = ss->lastseen;

    return ss;
}

/*
 * pickss - pick the next stateset to be used
 */
static struct sset* pickss(struct vars* v, /* used only for debug flags */
    struct dfa* d, chr* cp, chr* start)
{
    int i;
    struct sset* ss = NULL;
    struct sset* end = NULL;
    chr* ancient = NULL;

    /* shortcut for cases where cache isn't full */
    if (d->nssused < d->nssets) {
        i = d->nssused;
        d->nssused++;
        ss = &d->ssets[i];
        FDEBUG(("new c%d\n", i));
        /* set up innards */
        ss->states = &d->statesarea[i * d->wordsper];
        ss->flags = 0;
        ss->ins.ss = NULL;
        ss->ins.co = WHITE; /* give it some value */
        ss->outs = &d->outsarea[i * d->ncolors];
        ss->inchain = &d->incarea[i * d->ncolors];
        for (i = 0; i < d->ncolors; i++) {
            ss->outs[i] = NULL;
            ss->inchain[i].ss = NULL;
        }
        return ss;
    }

    /* look for oldest, or old enough anyway */
    if (cp - start > d->nssets * 2 / 3) { /* oldest 33% are expendable */
        ancient = cp - d->nssets * 2 / 3;
    } else {
        ancient = start;
    }
    for (ss = d->search, end = &d->ssets[d->nssets]; ss < end; ss++) {
        if ((ss->lastseen == NULL || ss->lastseen < ancient) && !(ss->flags & LOCKED)) {
            d->search = ss + 1;
            FDEBUG(("replacing c%d\n", (int)(ss - d->ssets)));
            return ss;
        }
    }
    for (ss = d->ssets, end = d->search; ss < end; ss++) {
        if ((ss->lastseen == NULL || ss->lastseen < ancient) && !(ss->flags & LOCKED)) {
            d->search = ss + 1;
            FDEBUG(("replacing c%d\n", (int)(ss - d->ssets)));
            return ss;
        }
    }

    /* nobody's old enough?!? -- something's really wrong */
    FDEBUG(("cannot find victim to replace!\n"));
    Assert(NOTREACHED);
    ERR(REG_ASSERT);
    return d->ssets;
}
